The present invention relates generally to methods of forming synthetic diamond or polycrystalline diamond (PCD). More specifically, the present invention relates to a new, high pressure-high temperature (HPHT) sintered/synthesized, self-grown, monopoly compact grit and methods of preparation thereof.
Diamond is a gemstone known for its rarity and beauty. As an industrial material, its superior hardness and wear resistance make diamond a preferred material in a variety of applications. For example, diamond is used extensively as an abrasive in polishing operations. Additionally, diamond-tipped drills and cutting tools are indispensable in shaping and cutting extremely hard materials such as sintered carbide and quartz. In order to help meet the industrial demand for these types of tools, a number of techniques have been developed for the production of synthetic diamonds. While natural diamond is still used in many industrial applications, diamond synthesis is emerging as the solution to the problem of inadequate supply of this unique material.
Diamond has a cube lattice, in which each carbon atom is covalently bonded to four other carbons to form a tetrahedron. This structure is repeated throughout the crystal and it is believed that this configuration of carbonxe2x80x94carbon bonds produces the extreme hardness of diamond. It has been discovered that at high temperatures and pressures, the conversion of carbon to diamond occurs at an appreciable rate. This phenomenon gave rise to the first synthetic high-pressure diamonds fabricated in the early 1950""s.
A synthetic diamond grit manufacturing method is disclosed in U.S. Pat. No. 2,947,609 (1960) to Herbert M. Strong, hereby incorporated by reference. A polycrystalline diamond compact with a metal bonded carbide substrate is described in U.S. Pat. No. 3,745,623 (1975) to Robert Wentorf Jr. et al, hereby incorporated by reference. Similarly, a polycrystalline cubic boron nitride with a metal bonded carbide substrate is disclosed in U.S. Pat. No. 3,743,489 to Robert Wentorf Jr. et al, also hereby incorporated by reference. A great deal of effort has been expended to increase the economy of preparing diamond grits under the HPHT conditions, however, commercial production of synthetic diamond grits, using the HPHT process is still a very expensive operation. Therefore, continuous attempts have been made both for the manufacturing of quality diamond grits and to develop an optimum HPHT diamond synthesis process for converting less expensive forms of carbon, such as graphite, into expensive diamonds.
There are two methods for the synthesis of diamond crystals at ultra-high pressure and high temperatures, which are generally well known in the art. The first method is the xe2x80x9ctemperature gradient method,xe2x80x9d and the second is the xe2x80x9cthin film solvent method.xe2x80x9d
The xe2x80x9ctemperature gradient method,xe2x80x9d involves using transitional metal elements, i.e. Fe, Co, Ni, Cr, Mn, Pt, etc. or alloys thereof, as a solvent metal. By this method, a diamond seed crystal is separated from a carbon source by the solvent metal so that the carbon source and the diamond seed crystal are not in contact with one another. By maintaining the temperature of the seed crystal at a relatively lower level than that of the contact surface of the carbon source and solvent metal, and allowing this assembly to stand at a high pressure and high temperature causes epitaxial growth of diamond on the seed crystal. See U.S. Pat. Nos. 4,034,066 and 4,632,817, which are hereby incorporated by reference.
The xe2x80x9cthin film solvent methodxe2x80x9d can be performed in two different ways. The first way consists of creating a reaction mixture of a non-diamond carbon source powder, a solvent metal powder, and seed crystal. The reaction mixture is then placed under temperature and pressure conditions in the diamond stable region, sufficient to convert the non-diamond carbon source into diamond in a relatively short time. The second way is by creating a reaction system which includes a plate of a non-diamond carbon source, or a laminate thereof, a plate of solvent metal, and optionally a seed crystal, and placing the system at a temperature and pressure within the diamond stable range, such that the non-diamond carbon source is converted into diamond within a relatively short period of time.
The above described temperature gradient method is capable of synthesizing a relatively large grain size crystal. However, it presents several problems. First, the synthesis reaction takes a very long time, thus increasing the operation costs of the apparatus required to affect the carbon to diamond transition. Additionally, because the method requires a temperature gradient to be created in a relatively small sample chamber, the number of crystals which can be produced in a single reaction is small. Therefore, the small crystal yield increases the production costs of each crystal.
The xe2x80x9cthin film solvent methodxe2x80x9d, solves many of the problems inherent in the xe2x80x9ctemperature gradient methodxe2x80x9d, but increases the frequency of other problems such as spontaneous nucleation. Such problems give rise to great difficulty in synthesizing crystals of a large grain size, and make the crystals produced inferior in quality as they may be contaminated with many inclusions.
In the typical diamond synthesis from carbonaceous materials utilizing a catalyst solvent material, a process for yielding a higher commercial quality valued diamond is the key to success. Needless to say, a higher commercial value diamond is directly related to both a higher product quality and a larger crystal size. The higher the crystal quality and the larger the size, the higher the value of the diamond. Product quality is generally graded according to the compressive and impact strength of the crystal. Crystal shape and internal clarity are also barometers of quality. A large size crystal is more valued as compared to a small size crystal. However, the manufacturing cost for growing larger diamond in the HPHT process is higher because of the required longer reaction/synthesis time and a relatively lower yield under HPHT conditions.
Large diamond crystals (up to 1.0 carat) are commercially produced using the technique of a seed diamond being placed in contact with the catalyst solvent and an available carbon source under long duration of high temperature and high pressure conditions. Such a process is cost and quality prohibitive from being utilized on a mass production scale.
The typical grit size which is used in the construction industry for items such as diamond saws and drill bits, is in the range of 20/30, 30/40, and 40/50 mesh. Although the current HPHT diamond synthesis processes have been significantly improved over a decade of active research and development efforts, these processes are still below desirable level for the efficient production of large crystals (20xcx9c50 mesh). Therefore, none of the current processes have so far been fully satisfactory in the super hard materials manufacturing industry.
Another problem inherent to many diamond grit applications such as diamond saw blades, grinding wheels and drill bits is obtaining a crystal shape which provides greater performance than that of existing crystals. Desirable shapes include cubic, octahedral, and needle-like shapes. The production of crystals having such shapes is not readily commercially available.
Yet another problem inherent in typical polycrystalline diamond (PCD) and cubic boron nitride compact (PCBN) applications, such as turning tools and wire dies, is producing ultra-fine grained (0.1xcx9c0.5 xcexcm) microstructure which provides a mirror-like surface finish to the product (optical lenses, aluminum, etc.). The production of such fine grained PCD or PCBN is not commercially and economically readily available.
For all intents and purposes, the quality and performance of diamond grits incorporated into tools such as saw blades, other cutting tools, and drill bits is primarily based upon the length of time which the grit will last under the impact and wear loads imposed thereon while being used in contact with a workpiece such as stone, concrete, or engineered materials. In fact, it has been discovered that shortened diamond grit performance is primarily due to the crushing effect imposed upon it by the workpiece rather than a wearing or abrading effect. Therefore, compressive and impact loading are key indicators of the potential performance of a diamond grit. Further, it has become well known that the impact strength of a single diamond crystal is far inferior to that of a polycrystalline diamond (PCD).
A xe2x80x9cself-grown monopoly compact gritxe2x80x9d, made by the process of this invention has unique physical properties as well as being economically feasible for large scale manufacture. Such a combination of advantages provides a significant improvement in the art of diamond synthesis. Particular areas of application of the crystals or PCD grits of this invention are the areas of saw blade, drill bit, cutting tool, dies, and grinding formations. In these areas, the impact strength of the diamond crystal provides a tool with greatly increased resistance to wear. Additionally, the crystals or PCD grits of the present invention may be formed in a number of desirable shapes in an economic and efficient manner.
Another well-known utility for synthetic diamond or cubic boron nitride (CBN) powders (60xcx9c230 mesh) is in the fabrication of grinding tools. Traditionally, grinding wheels have been fabricated according to the types of materials which they are intended to grind. In this arena, diamonds have been traditionally used for grinding non-ferrous containing material, while CBN grinding wheels have been widely used for grinding ferrous containing materials. Consequently, it would be desirable to have a material that is suitable for grinding both materials. By means of the present invention, a xe2x80x9cpolycrystalline diamond boron nitride gritxe2x80x9d (PCDBN) is synthesized from a combination of both diamond and CBN materials under HPHT conditions. This PCDBN possesses significant advantages over conventional CBN materials in ferrous material grinding tests.
It is an object of the present invention to provide a process for producing self-grown diamond crystals and/or monopoly compact PCD grits.
Another object of the invention is to provide stronger and more resilient diamond or CBN grits, as compared to conventionally grown diamonds or CBN grits. A further object of the present invention is to provide a method for producing improved diamond or CBN grits in a cost effective manner.
It is yet another object of the present invention to provide a process for the production of predetermined shapes of diamond or CBN compact grits in a cost effective manner.
Still another object of the present invention is to provide a new PCDBN compact grit product and a method of preparing the same.
These and other objects are accomplished by a self-grown monopoly compact grit produced from an improved HPHT process. The diamond or CBN grit produced by the HPHT process may be either a single crystal or a polycrystalline structure grown over a seed material. In each instance, the diamond or CBN compact grit is designed to be incorporated into a superabrasive industrial tool for cutting, drilling, machining, drawing, dressing, grinding, and/or polishing.
The basic process of diamond synthesis used by the present invention is similar to conventional diamond synthesis, (i.e. using a pressure-temperature-time cycle in the proper thermodynamic region with an available carbon source in the presence of a suitable catalyst solvent).
One aspect of the present invention is to provide a grown diamond crystal or PCD grit having a desired morphology. This synthesis process begins by obtaining a seed crystal and providing a suitable reaction site for controlling and maintaining diamond growth in such a manner that diamond nucleation does not take place. Another aspect of the present invention is to synthesize a new crystal (xe2x80x9cmonopoly compact gritxe2x80x9d) which is an as-sintered monopoly diamond with a polycrystalline diamond layer coated around a seed crystal.
According to the present invention, the improved HPHT process includes a series of special chemical treatments for the preparation of monopoly precursor materials which include metallic coating and fluidized bed granulation processes. By utilizing the newly designed HPHT process, it is possible to readily and reproducibly accomplish the manufacture of larger size (20xcx9c50 mesh) crystals at a reduced manufacturing cost. Additionally, the HPHT process of the present invention allows the manufacturing of grits in desirable shapes. Most importantly, the large crystals (20xcx9c50 mesh) have significantly improved crush strength over similar crystals produced by known HPHT processes. These enumerated advantages of the present invention culminate to provide a significant economic advantage over existing processes for manufacturing metal bond diamond grit products such as saw blades, drill bits and grinding tools.
The product of the present invention may take several different forms. For example, a PCDBN compact grit may comprise a newly grown diamond phase over a CBN seed. Further, either a CBN coating or a diamond phase may be grown over a PCD grit seed. The newly grown diamond phase is either a single crystal or a polycrystalline structure. The newly grown CBN phase can also be a single CBN crystal structure or a polycrystalline CBN structure.
In another aspect of the present invention, the monopoly compact grit is formed of the following optional materials: a seed crystal, a polylayer coating, and a reactive or non-reactive medium material. By using different combinations of materials similar products resulted.
The self-grown monopoly diamond, CBN, PCD, or PCDBN compact grits of this invention are made possible by an improved HPHT process comprising the following steps:
1) Preparing a Seed Crystal:
A crystal seed is properly selected for type (either diamond, CBN, or non-diamond), the size (50xcx9c270 mesh); and an optional coating (metallic or non-metallic). The seed crystal may include either a single mono-crystal or multiple crystals bound together to form a single composite multiple-grain seed. The optimal coating layer is prepared from conventional non-electrolytic, electrolytic, and pack-diffusion micro-vaporizing processes as well as spray type granulation processes, which are all well known in the art. Thus, the coating layer is either of a uniform coating thickness or in the form of a loosely packed fine coating powder.
2) Applying a Polylayer Precursor into the Seed Crystal:
A polylayer precursor is prepared by mixing diamond or CBN powders in a suitable bonding agent. The mixture is then applied onto the entire surface of the seed crystal through a counterflow liquid-gas fluidized bed diffusion process. To make a predetermined shaped precursor material, a subsequent simple shaping step can be applied to provide a desirable shape to the seed monopoly crystal.
3) Preparation of a Monopoly Precursor by the Packing of a Polylayer Precursor Coated Seed Crystal:
The monopoly seed crystal having been coated with the polylayer precursors is packed in a proper medium to form a monopoly precursor. The proper medium material is either reactive or non-reactive with diamond or CBN. A mixture of monopoly crystal and graphite powder and/or disc is one example. A mixture of monopoly precursor crystal and alumina powder is another example.
4) Application of Heat and Pressure for a Required Time:
The application of a specified amount of heat and pressure for a specified duration of time to the mixture of monopoly precursors and either reactive or non-reactive materials is required for the formation of the finished monopoly compact grits.
The above and other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings which are made in accordance with the present invention.